(1) Field of the Invention
This invention relates to a rubber formulation comprising (A) polymer ingredients comprised of (a) a hydrogenated nitrile rubber having a Mooney viscosity of up to 70 and (b) an organopolysiloxane, (B) a compound selected from (i) an unsaturated ester or polyester of acrylic acid or methacrylic acid with a polyhydric alcohol, (ii) an unsaturated amide or polyamide of acrylic acid or methacrylic acid with a polyamine, (iii) an alkoxysilane having a carbon-to-carbon unsaturated bond, amino group or a mercapto group, and (iv) triallyl isocyanurate, (C) an optional filler and (D) a peroxide crosslinking agent; a process for preparing this rubber formulation; and a crosslinked rubber formulation made therefrom.
The crosslinked rubber composition exhibits a good tensile strength, heat resistance, cold resistance and oil resistance, and therefore, is used widely in many industrial and chemical fields.
(2) Description of the Related Art
A silicone rubber has a good release property, heat aging resistance, cold resistance and weatherability, but as is known, the silicone rubber has a poor tensile strength, oil resistance and water resistance. Accordingly, use of the silicone rubber in the field where high mechanical strengths are required or in the field where the silicone rubber is placed in contact with oil or water, is restricted.
A hydrogenated nitrile rubber has a good tensile strength, oil resistance and heat resistance, but the hydrogenated nitrile rubber is not satisfactory in performances capable of coping with severe conditions of heat aging resistance, cold resistance and weatherability.
Accordingly, a combination of a silicone rubber and a hydrogenated nitrile rubber offsets the defects of the two rubbers, and it is expected that a satisfactory rubber formulation will be obtained by mixing together the two rubbers.
As the known technique of mixing a silicone rubber and a hydrogenated nitrile rubber, there can be mentioned a process wherein a silicone rubber is mechanically mixed with a hydrogenated nitrile rubber, as disclosed in German Patent No. 3812354. The mechanical mixing disclosed is a simple mechanical mixing conventionally employed in mixing together rubbers having a good compatibility with each other. However, a hydrogenated nitrile rubber has a poor compatibility with a silicone rubber and has a viscosity much higher than that of the silicone rubber. Therefore, even though the two rubbers are practically kneaded by the above mechanical kneading, it is difficult or even impossible to obtain a homogeneous rubber formulation. Further, the silicone rubber is different from the hydrogenated nitrile rubber in the induction time for the crosslinking reaction and the rate of crosslinking reaction, and therefore, it is difficult to obtain a homogeneous cured rubber product. The cured product of the rubber formulation of the two rubbers has unsatisfactory physical properties, and thus, advantageous characteristics of the two rubbers cannot be manifested.